Models are proposed predicting certain cellular interactions such as control of growth, cytopathic effects, inhibition of metabolism which occur between an insect (the cockroach Blattella germanica) and its intracellular procaryotic symbiote (Blattabacterium cuenoti). Tissue culture and rickettsiological procedures will be used to detect an infectious form of the symbiote. Analysis of the dynamics of symbiote penetration into the host cell will be used to elucidate the mode of infection, comparing it with the pathogenic intracellular parasites transmissible to vertebrates by arthropod vectors. Infected cultured cells and synchronized developmental stages of insects will be used to collect data, largely by particle counting procedures, to determine if symbiote growth correlates with, or is independent of, the host cell cycles. Kinetic aspects (e.g., migrations, infections) of the life cycle of the microorganism will be examined in greater detail using light and electron microscope techniques. Chemically defined diets will be used to identify the nutritional role of B-lactoglobulin, which is a very effective factor for survival and growth of the aposymbiotic cockroach. The transfer of nutrients through the isolated intestine will be monitored to test the hypothesis that the symbiote elaborates a compound (a peptide) which influences the permeability of host cells.